Ligaments are tough bands of tissue which serve to connect the articular extremities of bones, or to support or retain organs in place within the body. Ligaments are typically composed of coarse bundles of dense white fibrous tissue which are disposed in a parallel or closely interlaced manner, with the fibrous tissue being pliant and flexible, but not significantly extensible.
In many cases, ligaments are torn or ruptured as a result of accidents or overexertion. Accordingly, various procedures have been developed to repair or replace such damaged ligaments. For example, in the human knee, the anterior and posterior cruciate ligaments (i.e., the ACL and PCL) extend between the top end of the tibia and the bottom end of the femur. The ACL and PCL cooperate, together with other ligaments and soft tissue, to provide both static and dynamic stability to the knee. Often, the ACL is ruptured or torn as a result of, for example, a sports-related injury. Consequently, various surgical procedures have been developed for reconstructing the ACL so as to restore normal function to the knee.
In many instances, the ACL may be reconstructed by replacing the ruptured ACL with a graft ligament. More particularly, with such procedures, bone tunnels are typically formed in the top end of the tibia and the bottom end of the femur, with one end of the graft ligament being positioned in the femoral tunnel and the other end of the graft ligament being positioned in the tibial tunnel. The two ends of the graft ligament are anchored in place in various ways known in the art so that the graft ligament extends between the femur and the tibia in substantially the same way, and with substantially the same function, as the original ACL. This graft ligament then cooperates with the surrounding anatomical structures so as to restore normal function to the knee.
Two popular approaches to ACL reconstruction include a transtibial approach and an anteromedial approach. In the transtibial approach, a surgeon will first drill a tunnel through a tibia and insert a guide pin through the tunnel and through intra-articular space between a femur and the tibia to locate and drill an aligned femoral tunnel. Once the guide pin is placed, a reamer overdrills the guide pin and passes into the femur to create a final diameter of the femoral tunnel in which a ligament graft can be positioned and secured. Such an approach, however, can be difficult as the femoral tunnel entrance can be constrained by the position and trajectory of the tibial tunnel.
In the anteromedial approach, a surgeon inserts the guide pin directly into the femur through an Anterior Medial (“AM”) portal, which renders initial drilling of the tibia unnecessary. By reaming a femoral tunnel through the AM portal, the femoral tunnel entrance can be located closer to where the ACL was attached to the femur and thus, can result in a more anatomical ACL reconstruction. However, due to the “shallow” angle of approach directly into the femur, the trajectory brings the guide pin much closer to articular cartilage in the intra-articular space than in the transtibial approach. Since the reamer will have a larger diameter than the guide pin, it can be challenging to place the reamer over the guide pin without scraping or damaging the articular cartilage of the medial femoral condyle because of inadequate clearance in the anteromedial approach.
Accordingly, there remains a need for improved methods and devices for creating tunnels in bone.